design and implementation of dual voltage source …ijitech.org/uploads/261435ijit14142-94.pdfdesign...

WWW.IJITECH.ORG

ISSN 2321-8665

Vol.05,Issue.03,

March-2017,

Pages:0468-0475

Copyright @ 2017 IJIT. All rights reserved.

Design and Implementation of Dual Voltage Source Inverter with Power

Quality Improvement for Grid Connected Systems K. PURUSHOTHAM

1, K. RAJU

2

1PG Scholar, Dept of EEE, Chadalawada Ramanamma Engineering College, Tirupathi, AP, India,

Email: [email protected]. 2Assistant Professor, Dept of EEE, Chadalawada Ramanamma Engineering College, Tirupathi, AP, India,

Email: [email protected].

Abstract: This paper presents a dual voltage source inverter

(DVSI) scheme to enhance the power quality and reliability of

the micro grid system. The proposed scheme is comprised of

two inverters, which enables the micro grid to exchange

power generated by the distributed energy resources (DERs)

and also to compensate the local unbalanced and nonlinear

load. The control algorithms are developed based on

instantaneous symmetrical component theory (ISCT) to

operate DVSI in grid sharing and grid injecting modes. The

proposed scheme has increased reliability, lower bandwidth

requirement of the main inverter, lower cost due to reduction

in filter size, and better utilization of micro grid power while

using reduced dc-link voltage rating for the main inverter.

These features make the DVSI scheme a promising option for

micro grid supplying sensitive loads. The topology and

control algorithm are validated through extensive simulation.

Keywords: DVSI, ISCT, DERs.

I. INTRODUCTION

Technological progress and environmental concerns drive

the power system to a paradigm shift with more renewable

energy sources integrated to the network by means of

distributed generation (DG). These DG units with coordinated

control of local generation and storage facilities form a

microgrid [1]. In a microgrid, power from different renewable

energy sources such as fuel cells, photovoltaic (PV) systems,

and wind energy systems are interfaced to grid and loads

using power electronic converters. A grid interactive inverter

plays an important role in exchanging power from the

microgrid to the grid and the connected load [2], [3]. This

microgrid inverter can either work in a grid sharing mode

while supplying a part of local load or in grid injecting mode,

by injecting power to the main grid. Maintaining power

quality is another important aspect which has to be addressed

while the microgrid system is connected to the main grid. The

proliferation of power electronics devices and electrical loads

with unbalanced nonlinear currents has degraded the power

quality in the power distribution network. Moreover, if there

is a considerable amount of feeder impedance in the

distribution systems, the propagation of these harmonic

currents distorts the voltage at the point of common coupling

(PCC). At the same instant, industry automation has reached

to a very high level of sophistication, where plants like

automobile manufacturing units, chemical factories, and

semiconductor industries require clean power. For these

applications, it is essential to compensate nonlinear and

unbalanced load currents [4]. Load compensation and power

injection using grid interactive inverters in microgrid have

been presented in the literature [5], [6]. A single inverter

system with power quality enhancement is discussed in [7].

The main focus of this work is to realize dual functionalities

in an inverter that would provide the active power injection

from a solar PV system and also works as an active power

filter, compensating unbalances and the reactive power

required by other loads connected to the system. In [8], a

voltage regulation and power flow control scheme for a wind

energy system (WES) is proposed. A distribution static

compensator (DSTATCOM) is utilized for voltage regulation

and also for active power injection.

The control scheme maintains the power balance at the

grid terminal during the wind variations using sliding mode

control. A multifunctional power electronic converter for the

DG power system is described in [9]. This scheme has the

capability to inject power generated by WES and also to

perform as a harmonic compensator. Most of the reported

literature in this area discuss the topologies and control

algorithms to provide load compensation capability in the

same inverter in addition to their active power injection.

When a grid-connected inverter is used for active power

injection as well as for load compensation, the inverter

capacity that can be utilized for achieving the second

objective is decided by the available instantaneous microgrid

real power [10]. Considering the case of a grid-connected PV

inverter, the available capacity of the inverter to supply the

reactive power becomes less during the maximum solar

insolation periods [11]. At the same instant, the reactive

power to regulate the PCC voltage is very much needed

during this period [12]. It indicates that providing

multifunctional ties in a single inverter degrades either the

real power injection or the load compensation capabilities.

K. PURUSHOTHAM, K. RAJU

International Journal of Innovative Technologies

Volume.05, Issue No.03, March-2017, Pages: 0468-0475

This paper demonstrates a dual voltage source inverter

(DVSI) scheme, in which the power generated by the

microgrid is injected as real power by the main voltage source

inverter (MVSI) and the reactive, harmonic, and unbalanced

load compensation is performed by auxiliary voltage source

inverter (AVSI). This has an advantage that the rated capacity

of MVSI can always be used to inject real power to the grid,

if sufficient renewable power is available at the dc link. In the

DVSI scheme, as total load power is supplied by two

inverters, power losses across the semiconductor switches of

each inverter are reduced. This increases its reliability as

compared to a single inverter with multifunctional capabilities

[13]. Also, smaller size modular inverters can operate at high

switching frequencies with a reduced size of interfacing

inductor, the filter cost gets reduced [14]. Moreover, as the

main inverter is supplying real power, the inverter has to track

the fundamental positive sequence of current. This reduces

the bandwidth requirement of the main inverter. The inverters

in the proposed scheme use two separate dc links. Since the

auxiliary inverter is supplying zero sequence of load current,

a three-phase three-leg inverter topology with a single dc

storage capacitor can be used for the main inverter. This in

turn reduces the dc-link voltage requirement of the main

inverter. Thus, the use of two separate inverters in the

proposed DVSI scheme provides increased reliability, better

utilization of microgrid power, reduced dc grid voltage rating,

less bandwidth requirement of the main inverter, and reduced

filter size [13]. Control algorithms are developed by

instantaneous symmetrical component theory (ISCT) to

operate DVSI in grid-connected mode, while considering

nonstiff grid voltage [15], [16]. The extraction of fundamental

positive sequence of PCC voltage is done by dq0

transformation [17]. The control strategy is tested with two

parallel inverters connected to a three-phase four-wire

distribution system. Effectiveness of the proposed control

algorithm is validated through detailed simulation and

experimental results.

II. RELATED WORK

A. “Multifunctional VSC Controlled Microgrid Using

Instantaneous Symmetrical components Theory”.

This paper proposes a control scheme to control the

microgrid side voltage source converter (G-VSC) using

instantaneous symmetrical components theory. The G-VSC

with proposed control can be utilized I) as a bidirectional

power sharing converter to control the power flow from the dc

side to the ac side and vice versa, based on renewable power

available at the dc link. I) as a power quality compensator

with the features of reactive power compensation, load

balancing, and mitigation of current harmonics generated by

nonlinear loads at the point of common coupling, thus

enabling the grid to supply only sinusoidal current at unity

power factor III) to damp out the oscillations in the G-VSC

currents effectively using damping filter in the control

algorithm. The mathematical models are derived and stability

aspects are analyzed in detail through the frequency domain

approach.

B. “Interactive Distributed Generation Interface for

Flexible Micro-Grid Operation in Smart Distribution

Systems”. This paper presents an interactive distributed generation

(DG) interface for flexible micro-grid operation in the smart

distribution system environment. Under the smart grid

environment, DG units should be included in the system

operational control framework, where they can be used to

enhance system reliability by providing backup generation in

isolated mode, and to provide ancillary services (e.g. voltage

support and reactive power control) in the grid-connected

mode. To meet these requirements, the proposed flexible

interface utilizes a fixed power–voltage–current cascaded

control structure to minimize control function switching and

is equipped with robust internal model control structure to

maximize the disturbance rejection performance within the

DG interface. The proposed control system facilitates flexible

and robust DG operational characteristics such as 1)

active/reactive power (PQ) or active power/voltage (PV) bus

operation in the grid-connected mode, 2) regulated power

control in autonomous micro-grid mode, 3) smooth transition

between autonomous mode and PV or PQ grid connected

modes and vice versa, 4) reduced voltage distortion under

heavily nonlinear loading conditions, and 5) robust control

performance under islanding detection delays.

C. “Multifunctional VSC Controlled Microgrid Using

Instantaneous Symmetrical Components Theory”. This paper proposes a control scheme to control the

microgrid side voltage–source converter (G-VSC) using

instantaneous symmetrical components theory. The G-VSC

with proposed control can be utilized 1) as a bidirectional

power sharing converter to control the power flow from the dc

side to the ac side and vice versa, based on renewable power

available at the dc link; 2) as a power quality compensator

with the features of reactive power compensation, load

balancing, and mitigation of current harmonics generated by

nonlinear loads at the point of common coupling, thus

enabling the grid to supply only sinusoidal current at unity

power factor; and 3) to damp out the oscillations in the G-

VSC currents effectively using damping filter in the control

algorithm. The mathematical models are derived and stability

aspects are analyzed in detail through the frequency domain

approach.

D. “Advanced Control Architectures for Intelligent Micro

grids”. This paper presents a review of advanced control techniques

for micro grids. This paper covers decentralized, distributed,

and hierarchical control of grid-connected and islanded micro

grids. At first, decentralized control techniques for micro

grids are reviewed. Then, the recent developments in the

stability analysis of decentralized controlled micro grids are

discussed.

E. “Grid Interconnection of Renewable Energy Sources at

the Distribution Level with Power-Quality Improvement

Features”.

Renewable energy resources (RES) are being increasingly

connected in distribution systems utilizing power electronic

Design and Implementation of Dual Voltage Source Inverter with Power Quality Improvement for Grid Connected Systems



converters. This paper presents a novel control strategy for

achieving maximum benefits from these grid-interfacing

inverters when installed in 3-phase 4-wire distribution

systems. The inverter is controlled to perform as a multi-

function device by incorporating active power filter

functionality. The inverter can thus be utilized as: 1) power

converter to inject power generated from RES to the grid, and

2) shunt APF to compensate current unbalance, load current

harmonics, load reactive power demand and load neutral

current. All of these functions may be accomplished either

individually or simultaneously. With such a control, the

combination of grid-interfacing inverter and the 3-phase 4-

wire linear/non-linear unbalanced load at point of common

coupling appears as balanced linear load to the grid.

III. PROPOSED SYSTEM

A. Voltage Source Inverter (Vsi):

The main objective of this section is to recommend a

scheme that is best suitable for a given application.

Applications can be distinguished mainly based on their

power level and hence the switching frequency or by the type

of load. To achieve this goal several space vector modulation

schemes have been considered. The choice of these schemes

was governed mainly by the performance criteria described

above. Analysis was first performed for each of these

schemes to develop expressions and generate a series of

curves under various operating conditions. Then the circuit

was simulated in SABER to verify the expressions developed

and finally the modulation schemes were tested real-time on a

prototype inverter to verify the validity of both the analysis

and simulation. The first part of the thesis deals with three-leg

voltage source inverters (Fig1),which are standard inverters

providing three-phase three-wire output. Four space vector

modulation schemes are considered here. Their performance

with respect to for each of the above mentioned factors is

analyzed over the entire range of modulation index and for

varying load power factor angles. A novel procedure for the

calculation of THD has also been proposed.

Fig 1. Topology of a three-leg voltage source inverter.

The analysis is verified using simulation and experiments.

The second part of the thesis deals with four-leg voltage

source inverters (Fig.1.2), which are very attractive for

applications where three-phase four-wire output is required.

This topology is known to produce balanced output voltages

even under unbalanced load conditions [9, 10]. Due to the

additional leg, the number of topologies which this inverter

could assume is sixteen which is twice that of a conventional

three-leg inverter. The process of space vector modulation

and duty cycle calculation for this four-leg topology is

reviewed first. Then the techniques developed for the analysis

of three-leg voltage. Source inverter in the first part of the

thesis is used to analyze a four-leg voltage source inverter.

Three space vector modulation schemes have been addressed

here. Their performance with respect to THD and switching

losses is analyzed. The analysis is performed for both

balanced and unbalanced load conditions. For the balanced

case, the analysis is performed over the entire range of

modulation index and over varying load power factors. For

the unbalanced case two kinds of unbalance have been

considered 1) load power factor unbalance 2) load magnitude

unbalance. The analysis is verified using simulation.

Fig 2. Topology of a four-leg voltage source inverter.

B. Dual Voltage Source Inverter

1. System Topology

The proposed DVSI topology is shown in Fig. 1. It consists

of a neutral point clamped (NPC) inverter to realize AVSI and

a three-leg inverter for MVSI [18]. These are connected to

grid at the PCC and supplying a nonlinear and unbalanced

load. The function of the AVSI is to compensate the reactive,

harmonics, and unbalance components in load currents. Here,

load currents in three phases are represented by ila ,ilb , ilc and

respectively. Also,ig(abc ), iμgm (abc ), and iμgx (abc ) show grid

currents, MVSI currents, and AVSI currents in three phases,

respectively. The dc link of the AVSI utilizes a split capacitor

topology, with two capacitors C1 and C2. The MVSI delivers

the available power at distributed energy resource (DER) to

grid.The DER can be a dc source or an ac source with rectifier

coupled to dc link. Usually, renewable energy sources like

fuel cell and PV generate power at variable low dc voltage,

while the variable speed wind turbines generate power at

variable ac voltage. Therefore, the power generated from

these sources use a power conditioning stage before it is

connected to the input of MVSI. In this study, DER is being

represented as a dc source. An inductor filter is used to

eliminate the high-frequency switching components generated

due to the switching of power electronic switches in the

inverters [19]. The system considered in this study is assumed

to have some amount of feeder resistance Rg , and inductance

Lg .Due to the presence of this feeder impedance, PCC voltage




is affected with harmonics [20]. Section III describes the

extraction of fundamental positive sequence of PCC voltages

and control strategy for the reference current generation of

two inverters in DVSI scheme.

Fig 3. Topology of proposed DVSI scheme.

2. Design of DVSI Parameters

AVSI: The important parameters of AVSI like dc-link

voltage (Vdc ), dc storage capacitors (C1 and C2), interfacing

inductance (Lfx ), and hysteresis band (±hx) are selected based

on the design method of split capacitor DSTATCOM

topology [16]. The dc-link voltage across each capacitor is

taken as 1.6 times the peak of phase voltage. The total dc-link

voltage reference (V) is found to be 1040 V. Values of dc

capacitors of AVSI are chosen based on the change in dc-link

voltage during transients. Let total load rating is S kVA. In

the worst case, the load power may vary from minimum to

maximum, i.e., from 0 to S kVA. AVSI needs to exchange

real power during transient to maintain the load power

demand. This transfer of real power during the transient will

result in deviation of capacitor voltage from its reference

value. Assume that the voltage controller takes n cycles, i.e.,

nT seconds to act, where T is the system time period. Hence,

maximum energy exchange by AVSI during transient will be

nST. This energy will be equal to change in the capacitor

stored energy. Therefore 1

2C1 Vdcr

2 − Vdc 12 = nST

Where Vdcr and Vdc 1 are the reference dc voltage and

maximum permissible dc voltage across C1 during transient,

respectively. Here, S =5 kVA, Vdcr = 520 V, Vdc 1 = 0.8 *Vdcr

or 1.2 *Vdcr , n = 1, and T = 0.02 s. Substituting these values

in (1), the dc link capacitance (C1) is calculated to be 2000

µF. Same value of capacitance is selected for C1 .

The interfacing inductance is given by Lf = 1.6 Vm

4hx fmax Assuming

a maximum switching frequency ( fmax ) of 10 kHz and

hysteresis band (hx) as 5% of load current (0.5 A), the value

of Lfx is calculated to be 26 mH.

MVSI: The MVSI uses a three-leg inverter topology. Its dc-

link voltage is obtained as 1.15 *Vml , where Vml is the peak

value of line voltage. This is calculated to be 648 V. Also,

MVSI supplies a balanced sinusoidal current at unity power

factor. So, zero sequence switching harmonics will be absent

in the output current of MVSI. This reduces the filter

requirement for MVSI as compared to AVSI [21]. In this

analysis, a filter inductance (Lfm ) of 5 mH is used.

3. Advantages of the DVSI Scheme The various advantages of the proposed DVSI scheme

over a single inverter scheme with multifunctional capabilities

[7]–[9] are discussed here as follows:

Increased Reliability: DVSI scheme has increased

reliability, due to the reduction in failure rate of

components and the decrease in system down time cost

[13]. In this scheme, the total load current is shared

between AVSI and MVSI and hence reduces the failure

rate of inverter switches. Moreover, if one inverter fails,

the other can continue its operation. This reduces the lost

energy and hence the down time cost. The reduction in

system down time cost improves the reliability.

Reduction in Filter Size: In DVSI scheme, the current

supplied by each inverter is reduced and hence the

current rating of individual filter inductor reduces. This

reduction in current rating reduces the filter size. Also, in

this scheme, hysteresis current control is used to track the

inverter reference currents. As given in (2), the filter

inductance is decided by the inverter switching

frequency. Since the lower current rated semiconductor

device can be switched at higher switching frequency, the

inductance of the filter can be lowered. This decrease in

inductance further reduces the filter size.

Improved Flexibility: Both the inverters are fed from

separate dc links which allow them to operate

independently, thus increasing the flexibility of the

system. For instance, if the dc link of the main inverter is

disconnected from the system, the load compensation

capability of the auxiliary inverter can still be utilized.

Better Utilization of Microgrid Power: DVSI scheme

helps to utilize full capacity of MVSI to transfer the

entire power generated by DG units as real power to ac

bus, as there is AVSI for harmonic and reactive power

compensation. This increases the active power injection

capability of DGs in microgrid [22].

Reduced DC-Link Voltage Rating: Since, MVSI is not

delivering zero sequence load current components, a

single capacitor three-leg VSI topology can be used.

Therefore, the dclink voltage rating of MVSI is reduced

approximately by 38%, as compared to a single inverter

system with split capacitor VSI topology.

IV. SIMULATION RESULTS

A. Simulation Diagram

The entire control strategy is schematically represented in

Fig 4. Control strategy of DVSI is developed in such a way

that grid and MVSI together share the active load power, and

AVSI supplies rest of the power components demanded by

the load.




Fig 4. Schematic diagram showing the control strategy of

proposed DVSI scheme.

Time (s)

Fig 5. Without DVSI scheme: (a) PCC voltages and (b)

fundamental positiveSequence of PCC voltages.

Time (s)

Fig 6. Active power sharing: (a) load active power; (b)

active power supplied by grid (c) active power supplied by

MVSI and (d) active power supplied by AVSI.

Time (s)

Fig 7. Reactive power sharing: (a) load reactive power; (b)

Reactive power supplied by AVSI and (c) reactive power

supplied by MVSI.

Time (s)

Fig 8. Simulated performance of DVSI scheme: (a) Load

currents (b) grid currents

(c) MVSI currents; and (d) AVSI currents.

Time (s)

Fig 9. Grid sharing and grid injecting modes of operation:

(a) PCC voltage and grid current (phase-a).

Vo

ltag

e (v

) P

ow

er (

kW

)

Rea

ctiv

e P

ow

er

(kV

Ar)

Cu

rren

t (A

) C

urr

en

t (A

)




Time (s)

Fig 10. Grid sharing and grid injecting modes of

operation: pcc voltage and MVSI current (phase-a).

Time (s)

Fig 11. DC-link voltage of AVSI.

B. Fuzzy Extension

Fig 12. Simulation diagram showing the control strategy

of proposed DVSI scheme and its subsystem using Fuzzy

controller.

Time (s)

Fig 13. Active power sharing: (a) load active power; (b)

active power supplied by grid (c) active power supplied by

MVSI and (d) active power supplied by AVSI using Fuzzy

controller.

Time (s)

Fig 14. Reactive power sharing: (a) load reactive power;

(b) Reactive power supplied by AVSI and (c) reactive

power supplied by MVSI.

Time (s)

Fig 15. Simulated performance of DVSI scheme: (a) load

currents (b) grid currents (c) MVSI currents; and (d)

AVSI currents.

Vo

lta

ge

(v)

Cu

rren

t (A

)

Vo

lta

ge

(v)

Po

wer

(k

W)

Rea

ctiv

e P

ow

er

(kV

Ar)




Time (s)


operation: (a) PCC voltage and grid current (phase-a).

Time (s)


operation: pcc voltage and MVSI current (phase-a).

Time (s)

Fig 18. (a) DC-link voltage of AVSI and (b) zoomed view

of dc-link voltage dynamics during load change.

V. CONCLUSION

A DVSI scheme is proposed for microgrid systems with

enhanced power quality. Control algorithms are developed to

generate reference currents for DVSI using ISCT. The

proposed scheme has the capability to exchange power from

distributed generators (DGs) and also to compensate the local

unbalanced and nonlinear load. The performance of the

proposed scheme has been validated through simulation and

experimental studies. As compared to a single inverter with

multifunctional capabilities, a DVSI has many advantages

such as, increased reliability, lower cost due to the reduction

in filter size, and more utilization of inverter capacity to inject

real power from DGs to microgrid. Moreover, the use of

three-phase, three wire topology for the main inverter reduces

the dc-link voltage requirement. Thus, a DVSI scheme is a

suitable interfacing option for microgrid supplying sensitive

loads.

VI. FUTURE SCOPE

The Most Advanced Controllers Such As Fuzzy Network,

Artificial Neutral Networks and adaptive Instantaneous Power

Theory can be used for high power applications. It Can Also

used with micro controller based upqc To Make the System

More Effective than DSTATCOM.

VII. REFERENCES

[1] A. Kahrobaeian and Y.-R. Mohamed, ―Interactive

distributed generation interface for flexible micro-grid

operation in smart distribution systems,‖ IEEE Trans. Sustain.

Energy, vol. 3, no. 2, pp. 295–305, Apr. 2012.

[2] N. R. Tummuru, M. K. Mishra, and S. Srinivas,

―Multifunctional VSC controlled microgrid using

instantaneous symmetrical components theory,‖ IEEE Trans.

Sustain. Energy, vol. 5, no. 1, pp. 313–322, Jan. 2014.

[3] Y. Zhang, N. Gatsis, and G. Giannakis, ―Robust energy

management for microgrids with high-penetration

renewables,‖ IEEE Trans. Sustain. Energy, vol. 4, no. 4, pp.

944–953, Oct. 2013.

[4] R. Majumder, A. Ghosh, G. Ledwich, and F. Zare, ―Load

sharing and power quality enhanced operation of a distributed

microgrid,‖ IET Renewable Power Gener., vol. 3, no. 2, pp.

109–119, Jun. 2009.

[5] J. Guerrero, P. C. Loh, T.-L. Lee, and M. Chandorkar,

―Advanced control architectures for intelligent microgrids—

Part II: Power quality, energy

storage, and ac/dc microgrids,‖ IEEE Trans. Ind. Electron.,

vol. 60, no. 4, pp. 1263–1270, Dec. 2013.

[6] Y. Li, D. Vilathgamuwa, and P. C. Loh, ―Microgrid power

quality enhancement using a three-phase four-wire grid-

interfacing compensator,‖ IEEE Trans. Ind. Appl., vol. 41, no.

6, pp. 1707–1719, Nov. 2005.

[7] M. Schoharie, R. Coelho, R. Schweitzer, and D. Martins,

―Control of the active and reactive power using dq0

transformation in a three-phase grid-connected PV system,‖

in Proc. IEEE Int. Symp. Ind. Electron., May 2012, pp. 264–

269.

[8] R. S. Bajpai and R. Gupta, ―Voltage and power flow

control of grid connected wind generation system using

DSTATCOM,‖ in Proc. IEEE Power Energy Soc. Gen.

Meeting—Convers. Del. Elect. Energy 21st Century, Jul.

2008, pp. 1–6.

[9] M. Singh, V. Khadkikar, A. Chandra, and R. Varma,

―Grid interconnection of renewable energy sources at the

distribution level with power-quality improvement features,‖

IEEE Trans. Power Del., vol. 26, no. 1, pp. 307–315, Jan.

2011.

[10] H.-G. Yeh, D. Gayme, and S. Low, ―Adaptive VAR

control for distribution circuits with photovoltaic generators,‖

IEEE Trans. Power Syst., vol. 27, no. 3, pp. 1656–1663, Aug.

2012.

Authors Profile:

K. Purushotham currently pursuing his

Postgraduate in Power Electronic and Drives in

Chadalawada Ramanamma Engineering College,

Tirupati, A.P. He has received her Bachelor

degree in Electrical and Electronics Engineering from sree

Vidyanikethan Engineering college Tirupati. A.P in 2012, and

K. Raju has received his M.Tech in Electrical

Power Systems from JNTUA college of

Engineering, Pulivendula in 2014. He received

his Bachelor Degree in Electrical and

Electronics Engineering from from Sri Sai

Institute of Technology and Science in 2010. He is currently

Cu

rren

t (A

) C

urr

en

t (A

)




working as a Assistant Professor in Department of Electrical

and Electronics Engineering, Chadalawada Ramanamma

Engineering College, Tirupati, A.P. His area of interests are

Deregulated Power System,,power System Stability.

design and implementation of dual voltage source …ijitech.org/uploads/261435ijit14142-94.pdfdesign...

Documents